Walker was released by the Rabbitohs last month and has joined Sydney rivlas the Sea Eagles.
The 21-year old was a part of Souths’ 2014 grand final-winning side and represented Australia four times last year.
Walker debuted in the NRL in 2013 and has scored 33 tries in 62 matches. The Mascot Jets junior is expected to play in the number 6 for Manly.
“Five-eighth was my favourite position coming through the juniors and if the coach wants me there I will jump at the opportunity.
“I’m excited to be at such a great Club – once I was moving from Souths, the Sea Eagles was my first and only priority.
“I’m delighted I am now a Sea Eagle.”
With Kieran Foran leaving Manly for Parramatta, Walker will partner Daly Cherry-Evans in the halves.
The Kangaroo outside back was let go by South Sydney after he was involved in a prescription drug overdoe with teammate Aaron Gray.